Television



J. N. DYER TELEVISION May 25, 1943.

Filed Feb. 24, 1941 5 Sheets-Sheet l (Green) INVENTOR John N Dyev WW( 0xff/2l ATTORNEY-5 J. N. DYER TELEVISION May 25, 1943.

Filed Feb. 24, 1941 s sheets-sheet 2 @W Ty ND WN. m .n .n 0 TJ BY l @d ATTORNEYS May 25, 1943. J. N. DYER TELEVISION Filed Feb. 24, 1941 @a y J4 Wy/x l, @l v .f/ /1 J/ i f f ff L- ff/ J4 lNvENToR Joh n N. Dyer ATTO RNEY5 Patented May ..1943

UNITED STATE TELEVISION John N. .Dyer, Stamford. Conn.. assignor to Columbia Broadcasting System, Inc., New York, N. Y., a corporation'ot New York Application February 24, 1941, 801101100. 380,097

' f 1 claims. (c1. 17a-'5.2)

This invention relates to television, especially to television in natural colors, The invention particularly relates to apparatus ofthe type employing ,rotating illter elements, and contemplates the provision of a form ofrotating element and arrangement of the rotating element-with respect pto-a cooperatingV scanning device which will yield a compact assembly adapted to be `conveniently housed in a cabinet, etc.

In colortelevision systems in which the object ieldis scanned successively in a plurality of colors and the signals transmitted to the receiver for reproduction, the use of rotating disks have heretofore been suggested. Suitable disks having segments of novel design are described in an ap" plication of Peter C. Goldmark, Serial No. 355,839,

disks are employed.v Also, the viewing'areafn'iay".Y

This latter feature is important since it ishig'hly`l desirable to keep the components as small 'as' 'Ios` led September 7, 1940, for Color television.

Such disks have been found to be quite satisfactory fromv the standpoint of operation. However, the diameter ofthe disk must in general be at least twice that of the scanning areafand the axis must be at one side of ythe scanning area.

Hence this requirement is alimiting factor in the design of a cabinet. For example, in a receiver employing a cathode ray tube, thetube must be located at one side of the axis of the disk. If the cabinetis kept down to minimum dimensions, this means that the viewing area will be at one side of the cabinet. Also, the diameter of the disk vdetermines the minimum width of the cabinet.

The present invention especially contemplates the provision Iof apparatus which will permit more freedom in the design of a compact,` attrac` tive cabinet. l y

The use of rotating iilter drums instead -of disks has been suggested in an application of Peter C. ',Goldmark, Serial No. 370,008, illed December 13,v 1940, and entitled Television The present application discloses various improverments in the design and construction of color` filter drums or, more generally, endless color iilter elements, and also in their assembly with cooperating scanning devices.

'In'. accordance with one feature of the invention,l the endless color filter element or band, preferably a drum, is arranged to encircle part or all of anv electronic scanning device. In the case of a receiver, a specic embodiment discloses a color filter drum encirclingwa cathode-ray, tube and `rotating about a horizontalaxis.V With such a construction and arrangement ythe width of.k thellter element need be only slightly greater than that of the scanned area. and hence the cabinet may be made much narrower than when sible without (sacriilcingviewing angle or otl'ierA tolerances.4

Thedimensions ofthe drum and thev in'lfrlber offllter segments may be selected so that the spacing -between'illters is equal to the l'ieightfofj the scanning area; plus a' distance to allow' for the blanking perod (about 10% at the 'p1-esenti?k time).-v In ksuch case, with proper phasing, the leading edge of` agiven filter segment may be made to traverse the scanning area at substa`n' tiallyl the same speedasthe scanning beam, and

coincide vtherewitl'hyHowever, it is found that with non-storage scanning devices, or scanning] devices of the type in .which the storage'eect persists for only part of the scanningv period, this relationship need not be. maintained. l`Ifthe` dimensions. of the drum or other moving filter element be properly selected so that the speed and .height of the illter segments' are properlyr correlated with the scanning, the height off'the filterV segments may be considerably less thanl the sum of the height of the scanning area pluslan' allowance forblanking. ,This permits the use' of a greater number of lter segments for a givenA length of the movingy element, and hence a re duction in the speed thereof. Such a reduction is highly advantageous'to avoid noise.

In accordance with another speciflc feature of were. parallel to the axis. This permits amore convenient mechanical arrangement in some cases. Y l Y; Y lInaccordance with a further feature of the irl-v vention, `a combination of a lter drum, a mirror and a projection cathode-ray tube is provided ,for

the projection ofY television imagesin color. The combination is arranged in anovel manner so that the filter drum cuts ci! a minimum amoun of light. l

The invention will be more fully understood by reference to the specinc embodiments illutrated in the drawings and the following description thereof. In the drawings:

Fig. 1 is an elevation of a specific embodiment in which* a cathode-ray receiver tube is completely encircled by a color illter drum;

Fimilisafrontviewofthe Fiml: v v

l"lg.3iss.dis.gramillustratingtheprinciplesl onwhichtheheightofaiilteranditsspeedof movement may be correlated with the verticalmentemployingadmmwithhelicallyshaped' filter segments; and

Figs.11and12areplanandfrontviews.re spectively. of anembodimentsimilar toFigs.8- in which' a t drum is employed instead ofaa-seamentdrum.

Referring to Figs. 1 and 2, a cathode-ray receiving tube having an envelope il. electron gun structure il, horizontal and vertical coils il, focussing coil i4 andluminescentscreen 'llisprovidem Thescanningeleetronbeam il isdenectedbythedeectingcoilstoscanascanning areai1(l"ig. 2) of the lumincent senesi onthefaceofthetubeinaseriesofhoriaontal side-by-side linesbeginning at thetop of the scanningarea'andptothebottom (or viceversa) inaileldscanningperiod. Duringa field scansion the scanning lines may be contlguomsothatallpointsoftheareaarecovered. or theymaybenon-contiguoussothatonlya single interlaced set of linesis covered. The othersetsofinterlacedlinesmaythenbescanned during succeeding field-scanning periods. Preferably. successive field scansione correspond to diii'erent primary colors. For example. the systemsdisclosedinthe application ofPeter G. Goldmark, Serial No. 355,840, tiled September '1. 1940, for Color television may be employed. in order thateachsetofinterlacedlinesmaybereproduced in each color within a complete cycle. Of

course, any other scanning system may be employed if desired, the present invention not being limited to any particular system.

Encircling the cathode-ray tube is a color nlter drum 2i. Thisdrumisrotatableaboutanaxisll andis driveninsynchronism withtheneldscanning by suitable driving means (not shown) Any desired means may be employed for synchronising the rotation of the drum with the held scan- Drum 2i is provided with a plurality of diilerent color filter segments, IIR, NG, 24B arranged around the peripheral surface of the drum. In the specific embodiment shown. the boundaries 25 betweensegmentsareparallelwiththedrum axis. I'brsystemsinwhichtheima'geaofsuccessive neld are exhibited in successively different colors, the number of iilter seg-l ments and the speed of rotation are selected so that the segments traverse the area Il at a frequency equal to the field-scanning i'requency. Y

It has previously been suggested to make the spacing of the illter segments around the periphery of the drum (that is, the separation of corresponding points such as respective leading edges) equal to the height of Il plus an allowance for' the blanking period (usually about 10% at the present time). In this manner the filter segments traverse the scanning area at substantially the same speed as the beam in the low frequency direction so that, by

propel phasing. `the boundaries between adjacent nltersegments may be made to coincide with the line being scanned so as to prevent color carryover and permit equal exposure of all areas through a filter of given color. Of course, if the peripheral surface is not closely vadjacent the scanning area. a suitable correction may be made. aswiilbeunderstoodbythoseintheart.

ThedrumofFig. lmaybeconstructedinthe foregoing manner, in lwhich case theassembly illustrated has the advantages of being more compact and more suitable for commercial assemblies than the arrangements heretofore suggested. However. with cathode-ray tubes in which the period of afterglow is brief, or decays to a negligible value in a fraction of a neldning period. it has been foundthat the spacing between successive filters may be less than that required above. thus permitting more iilters to be arranged on the peripheral surface of the drum and hence requiring a lower speed of rotation.

`Referring to Fig. 3, the saw-tooth waves 2l represent the displacement of the scanning beam in the vertical or low frequency direction, plotted against time. The scanning beam starts at Il. corresponding to the line at the top or bottom of the picture as Vthe case may'be. It

progresses over the lines of the scanning area until it reaches point 20, whereupon it returnsl abruptly to its initial value. The vertical distance' between points 2l and Il therefore represents the height of the scanning area Il (Fig. 2). Of course, in interlaced scanning the scanningbeamwillnotreturnwexactlythesame line at the end of each scanning period. but the difference may be disregarded for present purposa.

Three filter segments SIR, IIG and IIB are illustrated at the beginning of the field period corresponding to a red image. These same filter segments are illustrated at IIR', SIG', SIB' at the end of the same iield period. In order that the filter segments may occupy the same positionrelativetothescanning areaatthebeginning of their respective field periods, the distance a filter moves in a eld scanning period should equal thel distance between successive ltei segments. With no allowance for the Width of the boundaries. this is equal to the height of the nlter segments. as shown in Fig. 3. The traversal of the scanning area by a given lter is substantially linear. so that the dotted lines $2 and Il indicate the position of the leading and trailing edges of the red illter at any instant in the field scanning period. Since line 21. representing the position of the scanning beam, lies between the dotted lines l2 and Il throughout the ileld period,- the line being scanned .will alwavs be presented through the redillter.

yscanned is i beam, as 'shown in Fig. 4.

always presented through the green filter. j e n.

In Fig.Y 3 the red filter is always somewhat in advance .of thel line being scanned, the dierence varying from'a maximum at'the beginning of the scanning period (equal tothe height of the filter segment) to a minimum at the end of the scanning period. `In order to allow rfor a short of the filter segments, the separation thereof and the speed of travel thereof, a given lscanjning line may be obscured by. a filter of vgiven -color for any desired fraction of a field period.

With the proportions illustrated ,in Figs. 3 and 4, the phase of. the filter svegmentswith respect to the scanning beammay be varied between the v position shown in Fig.'3 and that :shown in Fig.

4. .With tubes of little or .no afterf-glow, this tolerance permits adjusting the phase so that the picture can be viewed from various angles" above and below the scanning area, and also avoids the necessity for precise phasing. vWithv tubes possessing after-glow, the :distance -34 may be madesufilcient to provider for `the after-glow and other desired tolerances.

Generally,` inI order that,y with .proper phasing,

eachy line of the scanning area may be obscured by a filter of given color asthat-line is scanned,

the sum of the height of the lter segment: plus the distance the segment moves in` a field period should be equal to or. greater than the sum of theheight .of the scanning area plus the allow' ance: for= blanking. If greater, tolerances for after-glow, phasing, etc. areobtained. This api plies for uniform movement `of the lter segments and linearl scanning, with thelter `segments closelyk adjacent the scanning area. If these conditions .are departed from, the :necessary variations may be taken into account by plottingr diagrams similar to Figs. 3` and/4 in which the actual positions of the lter segments l and scanning beam Iat each instant are indi"- While particularly applicable to afrotating filter drum. it willi be appreciated that the' principles of' Figs. 3 and 4` mayalso' be applied to lother endless filter bands, disks, etc.` y

It willl be noted that the vverticalheight the observers point of viewvdetermines the particular portion of the luminescent screen which he sees at any instant through a given lter segment. By'placing the cathoderay tube-inside-r the lter drum rather than outside thereof," so

that the concave surface of the'drum vis toward the tube, the tolerance inthe 'vertical'l viewing angle is increased. l'I'his isnya.y considerabl'eladvantage since a color filter lelement isffunavoidablyrather bulkyvand every effort is made `to reduce 'the size without sacrificing correct operation.

-, `iteierringnow to Figs. n

ment is illustrated which is especially applicable "547, speelde embodif I lto'fthe projection of images formed'by a cathoderay tube. A cathode-ray receiver tube.k 4l, forming an image kon the luminescent` surface v 42 thereof, is employed. This tube may be similar -to that of Fig. 1, but is preferably of va type which produces a small but very brilliant image.

I the concave lmirror 43 and reflected through the Light from the projector tube 4I isfreceived by lens 44 to a suitably positioned screen 45. Lens 44 is designed to correct for the aberrations of the miror 43. The mirror 43 and lens thus function iny a manner similar to that of the socalled Schmidt camera." yfamiliar in connection with ,astronomical instruments.

AA lter drum 46 is positioned with its peripheral surface closely adjacent the scanning area 42 of the vprojector tube, and with at least a portion of f its peripheral surface between the scanning area and the mirror 43. Although the drum could be positioned to encircle the projector tube Il., as illustratedin Fig. l, in order toavoid impeding the light rays as much as possible, the invention .contemplates positioning the mirror and. drum so proper filter.

trai portion ofthe mirror is reflecting, light rays that the surface of themirror extends within the drum. This arrangement is shown in Figs. 5-7. HAs shown in Figs. 6 and '.7. the-lterdrum vimpedes the rays of light through only a relatively narrow vertical band. The drum is preferably positioned lso that the filters pass as closelyv as possible to thel image so that all rays of light which reach the mirror will pass through the It will be apparent that if the centherefrom will be reflected through'various parts of the periphery of the drum lying within the mirror at any given instant. If the filter in front of the projector tube 4I is, say, red, such reflected A. rays whichimpinge on green or blue filter segments'will be absorbed and hencewill not impair thefcolor reproduction. If the reflected rays impinge onga red lter, they will .bey partially attenuatedl and then'allowed to:pass.. With a large number of filter segments-.this attenuation may not be objectionable. Howevenif desired,:suit

' able ,stationary masks may be placed inside those portions ofthe drum lying between the..mirror and the projector tube 4I, so as to cut off rays which would otherwise pass `through the periphery of the drum. e f

The number of lter segments may be selected as desired, six groups of three red, green and, blue filters being vspecifically illustrated. 1 l

' The drum may be supported` and driven by suitable'bearings 41 as shown. Driving .power may be supplied to pulley 48, or in any other desired manner. Or, a vertical central slice may `be cut out of the mirror to. allow the periphery of thedrum to be attached to a central axle,A and 6.0supwported andl driven thereby. When such a v slice-is-.cut out, it will be understood thatv the surface of the mirror may'still'bev considered to pass withinthe drum. p xV V'I'he'mirror and drum maybe *proportioned so that the mirror lies entirely within the 'drum in the vertical plane, or the ,mirrorgmayextend somewhat beyond the surface of .the drum as shown in Fig. 5. In such case suitableslots v49 may be provided in the surfacev of the mirror.

f-In either case/those portions of themirrorwhich extend laterally from thedrum (see Fig. 6) f will receive light raysfrom the;projector tube and reectthem to the vscreen 45. If desired, the mirror may be wider than. it is, high so as Ato provide more light gathering power.

Broadly speaking. although a rotating illter dnnnsuchasillustratedinI'lgs.5-'l isadvantag'eous, any desired endless lter band may be employed.

Referring now to Pigs.' 8-10. aV cathode-ray receiver tube 5I is employed comprising a bulbous portion l2 at one end of which is the luminescent screen I8. and an elongated neck I4 pro- Jectingat an angle from the other end of the bulbous portion. I 'he electron gun structure Il is arrangedwithintheneckllforsupplyinga scanning cathode-ray beam. Suitable deilectlng means (not shown) are of course employed, and causesthebeamtoscantheareallfromtopto bottom (or vice versa) in horizontal side-by-side lines. A color iilter drum `Il is arranged to encircle the bulbous portion of the cathode-ray tube. This general construction and arrangement has been suggested by Peter C. Goldmark and is described in his copending application died concurrently herewith.l

In accordance with the `present invention. the nlter drurn is arranged to rotate about a vertical axis 51 and the filter segments are arranged around the peripheral surface of the drum inthe form of helixes. This helical arrangement of filter segments permits the drum to be rotated about a vertical axis while a given filter segment follows the line scanning in the vertical direction so that the lines are exposed through the proper filter segment as they are scanned. Also, the cathode ray tube can be arranged with its elongated neck M extending from the bottom of the drum (or the top, if desired), rather than from the side thereof. Thus the arrangement may be advantageous from the standpoint of mechanical designandcabinetdesigninmany cases.

Any suitable number of\fllter segments may be employed as desired. Por three color reproduction, multiples of three will usually be desirable. In general the number of segments and the anguwith three\iilter segments. the angular twist '.'throughwhichtheiilterextends-inascanntng periodcanbeotherthanthatshown.,1'brexample, each segment could extend through 240. inwhichcasethedrumwouldberotatedthrwgh 240' in a scanning period. With this arrangement, aftera field Vscansioni with one filter has been completed, the next adjacent filter will not 1o ibut the secondsucceeding illter segment will be.

beinpositionforthebeginningofascansion.

IngeneraLitisbelievedpreferabletoarrange thenltersegmentssothatinaheightequalto thatofthescanningareaplusanallowancefor blanking, each segment twists through-an angle equ'altotheanglebetween adiacentiiltersegments. Inthis manner, the filter segments opk-erateinsnccessiorntlzespeedofrotationislolrlest. and maximum tolerances are obtained.

4ofthescanningareaplusadbtancetoallowfor blanking. `In this speciilc embodiment the chord 'Il of the segments is made substantiallyequal to thewidth ofthescanningareatokeepthediameter ofthe drumassmallaspossible. Ingeneral lt will be desirable to somewhat increase the diameter of the drum and circumferential length of the segments in order to provide desired toleriartvristofeachsegmentshouldbesuchthatasl the drum rotates the scanning lines are covered progressivelyastbeyarescanned,andso that when one field scanning is completed a iilter segment of diiferent color is in proper position to begin the next scansion. Although the arrangement and proportions of the helical segments may be varied widely to suit various conditions, the specific construction illustrated in Figs. 8-10 will be described for purposes of completeness.

Assumethatthe heightoftheiilterdrumis equal totheheightofthescanningpatternplus 10% to allow for blanking (present standards). Each helical Segment is arranged to twist through an angle of 120 from the top to the bottom of the drum. Then.ifthedrumisrotatedata uniform speed through 120 during a held-scanning period. the lines of the scanning area I8 will be progressively covered by. say. the red illterRasthelinesarescanneduniformlyfrom top to bottom. Atthe beginning of thenext ileld scansionthe greeniiltei-Gwillbeintheposition occupied by the red filter R in Fig. 9. Thus the lines will be progressively exposed through thev green nlter during that scanning period.v By

making the .chord il subtended by a given nlter somewhat greater thanthe width of the scanning area, suitable tolerances in lateral viewing angle, phasing. etc. may be obtained. Desired ing the angulartwist.

ances. v When drums having helically sha segments are employed with receiver tubes .samuel afterglow, the emmer-ent th or It will be apparent`that the drumshaving hellcally-shaped segments 'are not confined to the yparticular assemblies shown. Ingeneral, any

type of scanning device could be employed. If

desired the drumsocould be arranged to completelyencirclethetubeaslnllig.l,orarranged sotbatthetubeisentirelyoutsidethedrum. They could also be employed with transmitter yscanning devices such as electronic tubes. Also,

instead oftrue helixes, approximate forms could be employed.

Broadly, the drum has helical segments of different optical characteristics. and is arranged so that the segments ltraverse the scanning area in a direction which makes a substantial angle with vthe direction of low-frequencyscanning, and the boundaries between segments are at a substantial angle with respect to the direction of movement of the segments. Although a drum is preferred, othermoving elements could be employed if desired.

y In the preceding description the filter segments have been arranged to move fairly closely adjacentthe scanning areas. so that there is little or no magnification between the segments and scanning area. If an arrangement is selected such that magniilcation is present. it willbe understood that dimensions. speeds, etc., which are eifective at the scanning area may be selected, and suitable correction factors employed to find .y corresponding dimensions, speeds, etc.. elsewhere.

The foregoing specinc embodiments describe the use of drums in connection with receiver tubes. However, it will be apparent that similar arrangements may be employed in connection with transmitter tubes. the filter drum being arranged to encircle part or all of the tube. In the case of storage transmitting tubes, the dimensions may be selected so that the boundaries between filter segments substantially coincide with asiasos i side-by-side lines, a. "rotatable substantially ey the line being scanned so as to avoid color carryover, if desired.

The principles illustrated in Figs. 3 and 4 may be applied not only to the drum of Figs. 1 and 2, but also to the drums of the other g'ures as well. In general, features described in connectionwith one figure may also me employed with the others.

It will be understood that the present invention is not limited to the mere details of censtruction and arrangement of the parts disclosed, since many modifications may be made by those skilled in the art without departing from the spirit and scope of the invention.

I claim:

1. In natural color television, apparatus which comprises an electronic scanning device cpmprising an envelope having a two-dimensional scanning area therewithin, means for scanning said scanning area in two dimensions in a plurality of side-by-side lines at field-scanning frequency, a rotatable color filter drum having a yplurality of different color filter segments on the peripheral surface thereof, said drum encircling at least a portion of said envelope and being positioned so that as the drum rotates said color filter segments successively traverse said scanning area, and means for rotating said drum at a substantially uniform speed such that the eld of said scanning area is scanned during the period a lter segment traverses said scanning area.

2. In natural color television, apparatus which comprises an electronic scanning device comprising an envelope having a two-dimensional scanning area therewithin, means for scanning said scanning area in two dimensions in a plurality of side-by-side lines at field-scanning frequency, a rotatable color filter drum having a plurality of different color filter segments on the peripheral surface thereof, said drum encircling at least a portion of said envelope and being positioned so that as the drum rotates said color filter segments successively traverse said scanning area, and means for rotating said drum at a substantially uniform speed selected to cause said lter segments to traverse the scanning area at substantially field-scanning frequency.

3. In a color television receiver. in combination, a cathode-ray receiving tube having a luminescent screen therein and means for successively reproducing images on said screen in a plurality of side-by-side lines, a rotatable color lter drum having a plurality of color filter segments arranged around the peripheral surface thereof, said drum encircling at least a portion of said cathode-ray tube and the peripheral surface thereof moving adjacent said luminescent screen whereby light from the screen passes through the portion of the peripheral surface adjacent the screen, and means for rotating said drum to exhibitreproduced images on said screen successively in different colors.

4. In a color television receiver, in combination, a cathode-ray receiver tube having a luminescent screen therein, means for repeatedly scanning said screen at field-scanning frequency to reproduce images thereon in a plurality of lindrical color filter drum having a plurality of color filter segments arranged around the peripheral surface thereof withthe boundaries between segmentssubstantially parallel to the drum axis, said drum. encircling at least a portion of said cathode-ray tube and the peripheral surface thereof `moving adjacent said luminescent-screen whereby light from thescreen passes 'through the color lter segments as the segments traverse the Vscanning area, and means for rotating said drum at a substantially uniform speed selected to cause said filter segments to traverse the luminescent screen in the low-frequency direction at substantially field-scanning frequency to thereby exhibit successive images in successively different colors.

5. In a color television receiver, in combination, a cathode-ray receiving tube comprising an envelope having a bulbous portion and an elongated neck extending therefrom, an electron gun structure in said elongated neck. and a luminescent image-reproducing screen in said bulbous portion. opposite said elongated neck and substantially perpendicular to the axis thereof; means for deiiecting an electron beam from said gun to successively reproduce images on said 1uminescent screen in a plurality of side-by-side lines at field-scanning frequency, a. rotatable substantially cylindrical drum having a plurality of color filter segments arranged around the peripheral surface thereof with the boundaries between segments substantially parallel with the drum axis, said cathode-ray tube being positioned with said bulbous portion and neck within said drum and with said luminescent screen adjacent the periphery of the drum so that as the drum rotates the color filter segments successively traverse the luminescent screen and present images thereon successively in different colors, and means for rotating said drum at a uniform speed selected to cause said filter segments to traverse the luminescent screen at substantially field-scanning frequency.

6. Color television apparatus which comprises, in combination, an electronic scanning device comprising an envelope having a two-dimensional scanning area. therewithin, means for scanning said scanning area in two dimensions in a plurality of side-by-side lines at field-scanning frequency, a rotatable color filter drum having a plurality of different transparent color filter segments arranged around the peripheral surface thereof and positioned so that said segments successively traverse said scanning area in the low-frequency direction, and means for rotating said drum at a substantially uniform speed selected to cause said filter segments to traverse said scanning area at substantially field-scanning frequency, the effective height of a lter segment at the scanning area being less than the height of the scanning area and the sum of said effective height plus the distance traversed by a filter segment over the scanning area in a field-scanning period being equal to or greater than the height of the scanning area.

'7. In a color television receiver, in combination, a cathode-ray receiving tube having a luminescent screen therein'and means for successively reproducing two-dimensional images on said screen in a plurality of side-by-side lines at field-scanning frequency, a rotatable substantially cylindrical color lter drum having a plurality of color filter segments arranged around the peripheral surface thereof with boundaries substentieliyperalleitothelxmniddmmencirclinzetleutsportion ofsnidcsthode-rsy tube and the peripheral surtaee thereof moving edjeeent said luminescent screen whereby litht fremthescreenplssesthmxhthe portiqnofthe peripheral surface adjacent the screen. und means for rotating seid drum sta. substlntieily uniform speed selected to cause the nlter sesmentstotrnversetheimazeereestsubstantinlly nem-scanning frequency to exhibit reproducedimazesonssidscreensueoessivelyindif-- ferent colors, the elective height and speed of tnverseiofenitersesment ettheimseeerea. beinzlesthentheheizhtottheimazeueamd thespeedof treversalthereothythescanning beam in the low-frequency direction. vrespectively, and the sum of seid eilective height plus the distance traversed by l. sement in e fieldscenning period heinz 'equal to or greater than the height of theimage eres.

' JOHN N. DYER.. 

